In the health services organizations worldwide blood for homologous transfusion has always been and still is in short supply. Considerable amounts are used for transfusions on different indications, e.g., in connection to surgery on humans as mentioned above and in veterinary praxis. Blood is an expensive product due to the costs for collecting, testing and storing the same and the administration of the precise handling of the same. At homologous blood transfusions there is a risk of transferring detrimental diseases such as hepatitis, HIV infections, and different tropical diseases among others.
As an attempt to avoid the risks with homologous blood replacement, autologous blood transfusion has been suggested. In one autologous blood transfusion technique, the patient's own blood is collected during surgery from his surgical wound for a following re-transfusion of the “whole blood” when the patient will best need it. However, blood leaving the vascular bed will also get in contact with injured tissues forming the surgical wound's walls. This contact will activate the blood's coagulation.
When blood is sucked through a tubing system from a surgical wound into a blood collector the activation process will continue unless the internal surface of the tubing is blood compatible or until this process is stopped by an anticoagulant, such as a sodium citrate solution. Furthermore, it can not be avoided that air is also sucked into the system together with the blood. In fact much larger volumes of air are sucked than volumes of blood in the majority of the cases. The result is that almost all blood will pass through the system mixed with air as foam or froth until it has been defoamed.
It is important that the activation process resulting in polymerization or clot formation (coagulation) is stopped as early and complete as possible during that the blood is collected. This can only be achieved if an anticoagulant is added and mixed to the entire blood portion as early as possible during the blood collecting process. It should be noticed that the blood-air interface is not a blood compatible surface.
Beside blood and air the collected material may also contain non-desired tissue fragments from the surgical wound (clots, tissue fragments, fat, bone particles, etc.). These materials will also activate the same coagulation system during the blood collection process until the said system has been stopped (inactivated) by the added anticoagulant.
WO 01/14048 discloses a blood collection system comprising suction means for aspirating blood, a defoaming unit for defoaming the aspirated blood by virtue of subjecting the fluid to a G-force other than the force of gravity, a measuring device for in situ measuring the flow of the defoamed blood, a dosing means for dosing an additive, such as sodium citrate, into the blood at the output of the defoaming unit in dependence of preferably proportional to, the measured flow of the blood, a mixing unit for mixing the blood with the additive by virtue of subjecting the blood and the additive to a G-force other than the force of gravity, and a recipient for collecting the mixed blood and additive. The measuring device is an optical device arranged for measuring the amount of blood and the velocity of said amount, wherein the velocity is measured by recording the amount of blood in a first and in a second one-dimensional cross section of the tubing, located at different positions along the flow direction, at various times, and by correlating the recordings.